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A question was asked about a breaker tripping for a fire pump. Its a 1600amp breaker and its my understanding unless there is a short circuit, it should not be tripping, it is supposed to handle the locked rotor current indefinitely plus 100% of the other pump related accessories 2014 NEC 695.4(2).

The fire pump is a 200hp 460volt Code G motor. I know usually the lrc is around 6 times the flc of the motor in most cases. Its been a while since I had to do these calculations, but isn't something wrong with the breaker tripping like it is when there is no direct short found? The overload amps should have never been reached to tripped the breaker in my opinion.
 

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Is the breaker tripping or the overload? Did you put an amp meter on it? It could be the breaker or the motor if the breaker is tripping. Is the breaker an adjustable trip?
 

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You're right, it should not be tripping. Assuming 240A FLC, LRC should be around 1,440A. Are you sure the magnetic trips are set right? No GF trips? No shunt trips installed?
 

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The maximum locked rotor current for a code letter "G" motor would be 1513 amps based on Table 430.7(B).
Ah, I didn't look up the code letter. I did an ASS-u-me on the 600% of FLA as LRA. Silly me... :blink:

Lesson: pay attention to the details...
 

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Ah, I didn't look up the code letter. I did an ASS-u-me on the 600% of FLA as LRA. Silly me... :blink:

Lesson: pay attention to the details...
Well it could be as low as 1347 if you use the low end value for a code letter "G". The average of the low end and high end value would give you 1430, or almost exactly what you stated.
 
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